1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display device, a method of manufacturing a substrate for a liquid crystal display device, a liquid crystal display device and a method of manufacturing a liquid crystal display device. In particular, the present invention relates to correction of a defect in a liquid crystal display device substrate having a protrusion provided on an electrode for controlling alignment of the liquid crystal in order to increase the viewing angle.
2. Description of Related Art
A liquid crystal display device generally includes a structure having a liquid crystal sandwiched between a first substrate (referred to as “color filter substrate”) including a counter electrode and a color filter, for example, and a second substrate (referred to as “TFT substrate” or “active matrix substrate”) including a switching element such as TFT (Thin Film Transistor) and a pixel electrode, for example. The liquid crystal display device displays an image by applying a potential between the pixel electrode and the counter electrode to generate an electric field between these substrates and thereby control alignment of liquid crystal molecules by the electric field, and adjusting the amount of transmitted light from a backlight, for example, by controlling the alignment.
The liquid crystal display device has advantages such as thinness, lightweight and low power consumption, and has been used widely for electronic devices such as a monitor of a personal computer, a television receiver and a mobile phone. Regarding a liquid crystal display device having a relatively large screen size like those used for a monitor and a television receiver, vertical alignment (VA) mode with multiple domains (multi-domain) which is excellent in display quality such as luminance, contrast ratio and viewing angle characteristic, namely so-called MVA (Multi-domain Vertical Alignment) mode has become widespread. This is shown for example in Japanese Patent Laying-Open Nos. 2001-083523, 2001-021894 and 2001-109009.
The MVA mode provides a cut-out pattern (electrode opening) and a protrusion for controlling alignment of liquid crystal molecules (hereinafter referred to as “alignment control protrusion”) to the pixel electrode of the active matrix substrate and the counter electrode of the color filter substrate. The MVA mode uses a fringe field formed by the cut-out pattern and the alignment control protrusion and tilted alignment of the liquid crystal at the tilted portion of the alignment control protrusion so as to align liquid crystal molecules in a plurality of different directions within a pixel and to thereby increase the viewing angle.
Regarding the MVA mode liquid crystal display device having excellent display quality, there is a demand for a lower price. Various methods are being studied for reducing the price particularly by improving the manufacturing yield and reducing the manufacturing cost of the color filter substrate and the active matrix substrate which are components of the liquid crystal display device.
FIG. 13 is a plan view of one pixel of an active matrix substrate used for a conventional MVA mode liquid crystal display device. As shown in FIG. 13, the active matrix substrate has a plurality of pixel electrodes 51 arranged in a matrix form. In FIG. 13, the outline of pixel electrode 51 is indicated by a bold solid line. On each pixel electrode 51, an alignment control protrusion 58 is provided for implementing divided alignment of the liquid crystal. A scan signal line 52 for applying a scan signal and a data signal line 53 for applying a data signal are arranged to extend around each pixel electrode 51 and cross each other. In the vicinity of the portion where scan signal line 52 and data signal line 53 cross each other, a TFT 54 is provided as a switching element connected to pixel electrode 51. TFT 54 has its gate electrode connected to scan signal line 52 and a scan signal which is input to the gate electrode controls drive of TFT 54. Further, TFT 54 has its source electrode connected to data signal line 53, and a data signal is input to the source electrode of TFT 54. TFT 54 has its drain electrode connected to a drain lead line 55. The drain electrode of TFT 54 is further connected to an upper hold-capacitor electrode 55a via drain lead line 55, and to pixel electrode 51 via a contact hole 56. Upper hold-capacitor electrode 55a is one of two electrodes which are components of a hold capacitor element. A hold capacitor line (also referred to as “common hold-capacitor line”) 57 functions as the other electrode (lower hold-capacitor electrode) of the hold capacitor element.
FIG. 14 is a cross section along line XIV-XIV indicated by the arrow on the plan view of one pixel of the active matrix substrate shown in FIG. 13. As shown in FIG. 14, on a transparent and electrically insulating substrate 61 made of glass, plastic or the like, TFT 54 already shown in FIG. 13 is provided. TFT 54 includes gate electrode 62 and gate electrode 62 is connected to scan signal line 52 shown in FIG. 13. Scan signal line 52 and gate electrode 62 are produced by depositing a film made of a metal such as titanium, chromium, aluminum or molybdenum or depositing a film of an alloy of these metals or depositing a stacked film of these metals to a thickness of 1000 to 3000 angstroms by the well-known sputtering and patterning the film by the well-known photolithography. Hold capacitor line 57 functioning as the lower hold-capacitor electrode is formed in the same process step and made of the same material as scan signal line 52 and gate electrode 62.
A gate insulating film 63 (see FIG. 14) is provided on the whole substrate to cover gate electrode 62, scan signal line 52 and hold capacitor line 57. Gate insulating film 63 is formed of an electrically insulating film such as silicon nitride, silicon oxide or metal oxide film. On gate insulating film 63, a high-resistance semiconductor layer 64 made of amorphous silicon or polysilicon, for example, is arranged to overlap gate electrode 62. Further, on high-resistance semiconductor layer 64, a low-resistance semiconductor layer to be used as source electrode 65a and drain electrode 65b is provided as an ohmic contact layer. The low-resistance semiconductor layer is made of n+ amorphous silicon that is amorphous silicon doped with impurities such as phosphorus.
The insulating film and such films as amorphous silicon, polysilicon and n+ amorphous silicon films, for example, are deposited by the well-known plasma CVD (Chemical Vapor Deposition) for example and patterned by the well-known photolithography for example. The thickness of the gate insulating film may be 3000 to 4000 angstroms in the case where the film is a silicon nitride film, and the thickness of the high-resistance semiconductor layer may be approximately 1500 to 2500 angstroms in the case where the layer is an amorphous silicon film. The low-resistance semiconductor layer may be approximately 300 to 500 angstroms in thickness in the case where the layer is an n+ amorphous silicon film.
A data signal line 53 is formed to be connected to source electrode 65a. Drain lead line 55 and upper hold-capacitor electrode 55a are arranged to be connected to drain electrode 65b. Upper hold-capacitor electrode 55a is connected to pixel electrode 51 via contact hole 56 passing through an interlayer insulating film 67. Data signal line 53, drain lead line 55 and upper hold-capacitor electrode 55a are formed in the same process step. Data signal line 33, drain lead line 55 and upper hold-capacitor electrode 55a are produced by depositing a metal film such as titanium, chromium, aluminum, molybdenum, tantalum, tungsten or copper, a film of an alloy of these metals or a stacked film of these metals by the well-known sputtering for example to a thickness of 1000 to 3000 angstroms and patterning the film into a required shape by the well-known photolithography for example. TFT 54 is formed by performing channel etching by means of dry etching performed on the amorphous silicon film serving as the above-described high-resistance semiconductor layer and the n+ amorphous silicon film serving as the low-resistance semiconductor layer, using the pattern of data signal line 53 and drain lead line 55 as a mask.
Interlayer insulating film 67 is a resin film made of a photosensitive acrylic resin, for example, an inorganic insulating film made of silicon nitride or silicon oxide for example, or a stacked film of them. For example, a stacked film of a double layer structure is used that includes a silicon nitride film of 2000 angstroms in thickness deposited by the plasma CVD for example and a photosensitive acrylic resin film of 30000 angstroms in thickness formed by die coating (application) on the silicon nitride film.
Contact hole 56 extends through interlayer insulating film 67 formed to cover TFT 54, scan signal line 52, data signal line 53 and drain lead line 55. Contact hole 56 is formed, for example, by pattering the photosensitive acrylic resin film by the well-known photolithography (exposure and development) and etching the silicon nitride film by the well-known dry etching using the patterned photosensitive acrylic resin film as a mask.
Pixel electrode 51 is formed at an upper level of interlayer insulating film 67. Pixel electrode 51 is formed, for example, by depositing a transparent and electrically conductive film such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), zinc oxide or tin oxide for example, or a film of an alloy of them or a stacked film thereof by the sputtering, for example, to an approximately 500 to 2000 angstroms in thickness and patterning the film into a required shape by the well-known photolithography, for example.
On pixel electrode 51, alignment control protrusion 58 is formed as shown in FIGS. 13 and 14. Alignment control protrusion 58 is formed by applying a liquid resin onto the substrate by the well-known spin coat for example and patterning it through exposure, development and baking. The liquid resin may be phenol-novolac positive resist, liquid photosensitive acrylic resin or liquid photosensitive epoxy resin, for example. Alignment control protrusion 58 is formed with a film thickness (height) of 0.5 to 2.0 μm.
As shown in FIG. 13, alignment control protrusion 58 includes a main alignment control protrusion 58a and an auxiliary alignment control protrusion 58b (also referred to as “auxiliary rib,” “auxiliary protrusion”). Auxiliary alignment control protrusion 58b is disposed to overlap the upper side, lower side, right side or left side of pixel electrode 51 of the active matrix substrate. Auxiliary alignment control protrusion 58b is formed to extend from an end of main alignment control protrusion 58a. Auxiliary alignment control protrusion 58b is provided in order to help the divided alignment of liquid crystal molecules in the vicinity of the end of main alignment control protrusion 58a and the end of pixel electrode 51 and suppress generation of an undesired domain.
“Domain” herein refers to one of regions separated by protrusions or slits or refers to the state of alignment of liquid crystal aligned in one of regions thus separated. An undesired domain (hereinafter referred to as “undesired domain”) refers to a state where liquid crystal molecules are not in a desired state or not aligned in a desired direction in a boundary portion of the region and thus are aligned in various directions or aligned in an uncontrollable state, namely refers to an abnormal alignment state or a region where such an abnormal alignment state occurs.
Since auxiliary alignment control protrusion 58b is disposed to overlap the upper side, lower side, right side or left side of pixel electrode 51, it is disposed in a different direction from the direction in which main alignment control protrusion 58a is disposed. As a result, the alignment direction of liquid crystal molecules in the vicinity of auxiliary alignment control protrusion 58b is different from the direction of the divided alignment by main alignment control protrusion 58a. Therefore, liquid crystal molecules in the vicinity of auxiliary alignment control protrusion 58b make a relatively low contribution to the transmittance of the liquid crystal display device.
In order to suppress generation of an undesired domain and prevent decrease of the transmittance, auxiliary alignment control protrusion 58b is usually formed with the same or a smaller width as or than that of main alignment control protrusion 58a. This is for the purpose of providing the auxiliary alignment control protrusion with a smaller alignment regulating force than that of main alignment control protrusion 58a. 
FIG. 15 is a plan view of a color filter substrate used for a conventional MVA mode liquid crystal display device. FIG. 16 is a cross section along line XVI-XVI indicated by the arrow in FIG. 15. In FIGS. 15 and 16, the color filter substrate has a transparent insulating substrate 71 of glass or plastic for example on which a colored layer 72 is formed that includes a plurality of color layers, for example, a red (R) layer 72a, a green (G) layer 72b, a blue (B) layer 72c, and a black matrix (BM) layer 72d. 
Red (R) layer 72a, green (G) layer 72b, blue (B) layer 72c and black matrix (BM) layer 72d are formed in the following way. A resist solution (liquid resist) containing a pigment of each color is applied onto the substrate by the spin coat for example. Preparatory baking is performed to evaporate the solvent of the resist solution. The color layer film is thus formed on the substrate. A photomask is used to perform exposure and development and accordingly each color layer is patterned. The thickness of each color layer is usually 0.5 to 2.0 μm.
As shown in FIG. 16, a counter electrode 73 is formed on colored layer 72. Counter electrode 73 is formed for example by depositing a transparent and electrically conductive film of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), zinc oxide, or tin oxide for example, or a film of an alloy of them or a stacked film of them by the well-known sputtering for example to a thickness of approximately 500 to 2000 angstroms and processing the film as required into a desired pattern by the well-known photolithography for example.
As shown in FIGS. 15 and 16, an alignment control protrusion 74 defining the divided alignment of liquid crystal, and a photo spacer 75 having the function of making contact with the active matrix substrate opposite to the color filter substrate to maintain a cell gap in the completed liquid crystal display device are provided on counter electrode 73.
Alignment control protrusion 74 and photo spacer 75 are formed by applying a liquid resin onto the substrate by the well-known spin coat, for example, and performing exposure, development and baking. As the liquid resin, phenol-novolac-based positive resist liquid, photosensitive acrylic resin liquid or photosensitive epoxy resin liquid for example is available. The alignment control protrusion is formed to a thickness of 0.5 to 2.0 μm, and photo spacer 75 is formed to a thickness of 2.0 to 5.0 μm.
Alignment control protrusion 74 includes a main alignment control protrusion 74a and an auxiliary alignment control protrusion 74b (also referred to as “auxiliary rib,” “auxiliary protrusion”). Auxiliary alignment control protrusion 74b is disposed to overlap the upper side, lower side, right side or left side of black matrix layer 72d of the color filter substrate. Auxiliary alignment control protrusion 74b is usually formed to extend from an end of alignment control protrusion 74a. Auxiliary alignment control protrusion 74b is formed in order to help the divided alignment of liquid crystal molecules at the end of main alignment control protrusion 74a and suppress generation of an undesired domain.
Since auxiliary alignment control protrusion 74b is disposed to overlap the upper side, lower side, right side or left side of black matrix 72d, the auxiliary alignment control protrusion is disposed in a different direction from main alignment control protrusion 74a. As a result, the alignment direction of liquid crystal molecules near auxiliary alignment control protrusion 74b is different from the direction of the divided alignment defined by main alignment control protrusion 74a. Therefore, liquid crystal molecules near auxiliary alignment control protrusion 74b make a relatively low contribution to the transmittance of the liquid crystal display device.
In order to suppress generation of an undesired domain and prevent decrease of the transmittance, auxiliary alignment control protrusion 74b is usually formed with the same or a smaller width as or than that of main alignment control protrusion 74a. This is for the purpose of providing the auxiliary alignment control protrusion with a smaller alignment regulating force than that of main alignment control protrusion 74a. 
FIG. 17 is a cross section schematically showing an example of the conventional MVA mode liquid crystal display device. Conventional MVA mode liquid crystal display device 84 is configured to have an active matrix substrate 81 and a color filter substrate 82 that have respective alignment films (not shown) made of polyimide, for example, for aligning liquid crystal at the surface and that are attached to each other with a sealing material (not shown) at the peripheral portion so that respective alignment films (not shown) are located opposite to each other. At this time, the distance between the substrates (also referred to as “cell gap”) is kept constant by photo spacer 75. The portion between active matrix substrate 81 and color filter substrate 82 is filled with a liquid crystal forming a liquid crystal layer 83. A liquid crystal supply inlet is sealed with a sealing material (not shown). Alignment control protrusion 58 formed on pixel electrode 51 of active matrix substrate 81 and alignment control protrusion 74 formed on counter electrode 73 are disposed in a staggered configuration. With this configuration, liquid crystal molecules of liquid crystal layer 83 are arranged in the divided alignment form according to an applied potential.
The color filter substrate and the active matrix substrate are both liquid crystal display device substrates. As described above, the process of manufacturing an MVA mode liquid crystal display device substrate includes the step of forming an alignment control protrusion. In the step of forming the alignment control protrusion, such defects as partial absence of the alignment control protrusion and a remaining film of the alignment control protrusion could occur. In a pixel region where an absent portion or a remaining film portion of the alignment control protrusion occurs, the liquid crystal is not aligned normally. As a result, alignment failure or pixel defect (black spot or bright spot) occurs and the display quality deteriorates.
The alignment control protrusion is usually formed by patterning, using a liquid resist prepared by dissolving a phenol-novolac-type positive photosensitive resin in a solvent, applying the resist onto the substrate by the well-known spin coat and performing exposure and development. Alternatively, the alignment control protrusion may be formed by patterning, using, instead of the liquid resist, a dry film having a film-shaped support where a positive photosensitive resin film is formed, forming a resin film on the substrate by a thermal transfer process, and performing exposure and development on the resin film. Regardless of the manufacturing method, in this process of manufacturing, it is difficult to completely avoid the occurrence of such defects as absence and a remaining film of the alignment control protrusion due to dust on or scratches in the photomask which is used for exposure or foreign matter caught when the film is applied.
The auxiliary alignment control protrusion is usually formed with the same width as or a smaller width than that of the main alignment control protrusion in order to suppress generation of an undesired domain and prevent decrease of the transmittance. As described above, in the case where the positive photosensitive resin is used where an exposed portion is dissolved in a development solution, as the degree of exposure is larger, the pattern after development is likely to be thinner. Further, as compared with the negative photosensitive resin, the positive photosensitive resin is inferior in terms of adhesion to the substrate. Therefore, a thin auxiliary alignment control protrusion is more likely to become partially absent as compared with the main alignment control protrusion.
In the conventional practice, any substrate having a defect such as partial absence or a remaining film as described above was discarded as a defective product. Therefore, the manufacturing cost increases and the productivity decreases.
Some techniques concerning a method of correcting such defects as partial absence of a film and a remaining film have been disclosed. Japanese Patent Laying-Open No. 11-271752 discloses a method according to which ink for correction is dropped onto an absent portion of the film by the ink jet method. Japanese Patent Laying-Open No. 2003-273114 discloses a method according to which a photo CVD film is formed at an absent portion of the film. Japanese Patent Laying-Open No. 2000-331610 discloses a method of correcting partial absence of a barrier rib by applying a correction paste. Japanese Patent Laying-Open No. 2001-066418, Japanese Patent Laying-Open No. 2002-082217 and Japanese Patent Laying-Open No. 05-072528 disclose a method of removing a foreign matter or correcting the defect of a remaining film by irradiating the foreign matter or film-remaining defect with laser.
The above-described techniques are all related to a method of correcting a colored layer or counter electrode of a color filter substrate or a barrier rib of a plasma display, and they do not disclose a defect correction method for correcting an alignment control protrusion.
While techniques such as formation of a photo CVD film, dropping of correction ink and application of correction paste are disclosed regarding the partial absence of the film, the techniques all require another correcting material for correcting a defect in addition to materials used in a usual film-deposition process. Therefore, the efficiency of use of materials is low and development of a correction material is necessary.